An oxygen sensor may be used in a control scheme for regulating the supply of air and fuel to the cylinders of the internal combustion engine in such a way as to enable low-emission, energy-efficient operation.
The oxygen sensors currently used in the exhaust gas systems of motor vehicles usually encompass a ceramic layer, which is in contact with the exhaust gas flow on one side and with air on the other side. The ceramic layer, which is permeable to oxygen ions in a hot state, includes an electrode on each side. The electrodes deliver the electrons required for generating the oxygen ions. A resultant voltage between the electrodes can be tapped as a measuring signal, which provides information about the oxygen content in the exhaust gas.
The reaction time of such an oxygen sensor depends on how fast a fluctuation of the oxygen concentration in the exhaust gas affects the concentration of oxygen ions in the membrane; deposits on the membrane that impede the exchange of oxygen between the membrane and exhaust gas flow or ambient air, or that are able to store oxygen and release it again after a delay, can greatly prolong the reaction time, thereby impairing the quality with which the air-fuel ratio is regulated given engine load fluctuations.
In order to recognize such a situation and potentially prompt a user of the motor vehicle to remedy the latter, it is known to switch over to the cylinders in a deceleration phase of the motor vehicle within a timespan of several seconds between the supply of clean air and a rich mixture, and acquire the reaction time of the sensor to this change.
Such an approach is not feasible in automatic transmissions, which, when the driver takes his or her foot off of the gas pedal, decouple the engine from the gearing instead of decelerating, since the interruption of fuel supply would cause the engine to stop.
It also makes no sense to execute the switchover between the supply of clean air and a rich mixture in a partial load operation as described above, since an interruption in the fuel supply or even a reduction therein would limit drivability in a manner very tangible to the driver, and operation with a rich mixture would result in high consumption and pollutant emissions.